摘要:

AbstractNeuronal connections in the primary auditory cortex (AI) of the cat were studied electrophysiologically by using intracellular recording techniques. Fast‐conducting fibers from the medial geniculate nucleus (MG) projected monosynaptically onto AI neurons in layers III–VI (mainly in layer IV), whereas slow‐conducting MG‐fibers projected monosynaptically onto AI neurons in layer I. AI neurons which received monosynaptic inputs from the auditory association cortices (AII and Ep) and/or from the contralateral AI were distributed in all layers of the AI; the commissural fibers from the contralateral AI were divided into fast‐ and slow‐conducting ones.AI neurons were categorized into seven types: type I neurons which received monosynaptic inputs from slow‐conducting MG‐fibers were located in layer I. Type II neurons which received polysynaptic inputs from the MG were located in layers II–VI. Type III neurons which sent their axons to the AII or Ep were mainly located in layer III. Type IV neurons which sent their axons to the contralateral AI were located mainly in layer III. Type V neurons which received monosynaptic inputs from fast‐conducting MG‐fibers were located mainly in layer IV. Type VI neurons which projected onto the inferior colliculus were located in the upper part of the layer V. Type VII neurons which projected onto the MG were locat

ISSN:0092-7317    

DOI:10.1002/cne.902350402

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractThe morphology of electrophysiologically identified neurons was examined in the primary auditory cortex (AI) of the cat. After stimulation of the medial geniculate nucleus (MG), second auditory cortex, posterior ectosylvian gyrus, contralateral AI, or corpus callosum, intracellular potentials were recorded from AI neurons, which were then injected intracellularly with horseradish peroxidase and recovered.Layer IV neurons, which receive MG fibers monosynaptically, are spiny and nonspiny stellate cells, small and medium‐sized nonspiny tufted cells, and fusiform cells. They send their axons to layer III of the AI. Corticocortical AI neurons are medium‐sized pyramidal cells in layer III. They receive axons from layer IV neurons of the AI and send their axons to layers I, II, IV, and V of the AI. Horizontal cells in layer I receive slow‐conducting MG fibers monosynaptically, and send their axons to layer II of the AI. Stellate cells and small pyramidal cells in layer II receive afferent inputs polysynaptically from the MG. Layer II pyramidal cells receive afferent inputs from the MG via AI neurons in layers I and III, and send their axons to layers V and VI. The axons of layer II stellate cells were distributed within layer II. Pyramidal cells which send their axons to the MG are located in layers V and VI, distributing their axon collaterals to layers III–VI of

ISSN:0092-7317    

DOI:10.1002/cne.902350403

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractRecent studies (Cynader and Mitchell, '80; Mower et al., '81) have shown that total dark rearing prolongs susceptibility to the physiological effects of monocular deprivation (MD) in visual cortex beyond the normal age limits. The present study addressed whether this delayed physiological plasticity is accompanied by delayed anatomical plasticity in the geniculocortical pathway.Ocular dominance (OD) columns as defined by transsynaptic autoradiography following injection of3H proline into one eye were studied both qualitatively and quantitatively in 17 cats. Compared to normal rearing (N‐3), both binocular eyelid suture (N‐2) and total dark rearing (N‐3) resulted in incomplete segregation of OD columns in area 17. This apparent immaturity after binocular deprivation, however, did not reflect a delayed capacity for development and plasticity. Visual experience after dark rearing produced no marked changes. In cats who experienced MD after dark rearing, injection of either the nondeprived (N‐2) or deprived eye (N‐3) resulted in a nearly uniform distribution of label throughout layer IV of area 17. The same result occurred with binocular vision after dark rearing (N‐1). MD from birth, however, produced expansion of columns from the nondeprived eye (N‐1) and contraction of columns from the deprived eye (N‐1). MD imposed after 4 months of normal vision resulted in normal OD columns (N‐1).Electrophysiological studies revealed a high proportion of binocular cells within layer IV in cats who experienced monocular or binocular vision after dark rearing. Outside of layer IV there were clear environmental effects on OD of single cells in these cats. Measurements of cell sizes in the clateral geniculate nucleus showed shrinkage of cells innervated by the deprived eye when MD was initiated at birth (N‐3). MD after dark rearing (N‐4) produced no differences in cell sizes.It is concluded that (1) visual input is necessary for the formation of normal OD columns, (2) the critical period for formation and environmental modification of OD columns is limited to early life, and (3) the physiological effects of visual experience after dark rearing reflect changes occurring beyond the gen

ISSN:0092-7317    

DOI:10.1002/cne.902350404

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractA system of periodic intrinsic connections is demonstrated in area V2 (area 18) of squirrel and macaque monkeys by large injections of tritiated amino acids, horseradish peroxidase (HRP), and fluorescent latex beads. These connections originate from pyramidal neurons concentrated in layers 3 and 5. Terminations occur in all cortical layers, largely coextensive with labeled neurons but more restricted in layer 4. This multilaminar distribution contrasts with the mainly supragranular localization of periodic intrinsic connections in V1 (area 17), and may imply a close interaction, in V2, of periodic intrinsic connections with pulvinocortical, as well as with corticocortical terminations (concentrated, respectively, in layers 3 and 5, and in lower 3 and 4). As in V1, the tangential configuration of these connections in V2 is reticular or latticelike, and is detectable for 2.5–3.0 mm from an injection site of HRP,3H amino acids, or latex beads. Cross‐sectional widths of labeled regions vary from 250 to 800 μm in squirrel monkey and from 400 to 1,000 μm in macaque, depending on which portion of the lattice is measured. When periodic intrinsic connections are compared with stripes labeled histochemically by cytochrome oxidase (CO), no clear relationship is obvious between the two systems. This result contrasts with the orderly tangential alignment reported between CO‐reactive zones in V2 and certain extrinsic connections; namely, pulvinocortical terminations (Livingstone and Hubel, '82) and clusters of neurons projecting to area V4 (DeYoe and Van Essen, '84). Other extrinsic connections, however, such as backgoing connections from V2 to V1, do not seem to have a periodic distribution. Thus, although some discontinuous cortical connections relate to each other in a precise mosaic fashion, intrinsic and some extrinsic connections may observe different modes of organ

ISSN:0092-7317    

DOI:10.1002/cne.902350405

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractThe timing and positioning of occlusion of the spinal neurocele were studied in living and serially sectioned chick embryos at stages 8–14. Occlusion occurs in three phases: preocclusion, incipient occlusion, and definitive occlusion. Preocclusion occurs at stage 8. At this time, the neural groove of the spinal cord has not yet closed to form a neural tube. Incipient occlusion begins as early as stage 9 and lasts until stage 11. The neural groove of the cranial spinal cord closes during these stages and incipient occlusion occurs concomitantly with this closure. Seventy‐eight percent of the embryos exhibit incipient occlusion. Incipient occlusion extends along the mid‐somitic region of the neuroaxis, occupying about one‐half the length of the spinal cord. Injection of the brains of living embryos with dyes often reopens incipient occluded areas. Definitive occlusion occurs at stages 11–14 and is present in 89% of the embryos. Definitive occlusion is restricted to mid‐somitic regions, as was incipient occlusion, but it extends approximately two‐thirds the length of the spinal cord. Injection of the brains of living embryos with dyes rarely reopens definitive occluded areas, even when injection pressures are maximal. Six morphological types of definitive occlusion can be identified on the basis of the relative proportions and locations of total and partial occlusion. Closure of the cranial neuropore and roof plate of the hindbrian occurs near the end of the incipient occlusion phase, whereas closure of the caudal neuropore occurs well after definitive occlusion is initiated. Physiological occlusion is due to both anatomical occlusion and back pressure, which prevent the flow of liquids into a blind, narrow tube. Further studies are required to document the reopening phases of the spinal neurocele, as well as the forces involved in causing and maintaining occlusion

ISSN:0092-7317    

DOI:10.1002/cne.902350406

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractExperiments were done to test the hypothesis that individual ganglia of the myenteric plexus of the guinea pig small intestine are heterogeneous with respect to the location of the neurons that provide terminals to them. The myenteric plexus, attached to the longitudinal layer of smooth muscle, was maintained in vitro. Individual ganglia were injected with a variety of potential retrograde tracers by pressure microejection from the tip (20‐μm diameter) of a glass micropipette. The fluorescent dye 4‐acetoamido, 4′‐isothiocyanostilbene‐2,2′‐disulphonic acid (SITS) was found to be an effective tracer, labeling neuronal perikarya, evidently by retrograde transport. SITS has previously been shown not to cross plasma membranes, but to be covalently bound to the outer surface of that membrane, and to be taken up by nerve terminals to be retrogradely transported to label neuronal cell bodies. SITS fluorescence was found in about 12% of the neurons within the ganglion into which it was injected and also in approximately ten times more neurons in discretely located distant ganglia. No labeling of neurons was found when SITS was injected into the bath or into the smooth muscle below the myenteric plexus. Damage to neural connectives obstructed the labeling of neurons in ganglia distal to the injection site. Individual SITS‐injected myenteric ganglia were found to vary greatly in the ratios of intraganglionic SITS‐labeled neurons to the total number of neurons within the injected ganglion. The ratios of the number of intraganglionic SITS‐labeled neurons to SITS‐labeled neurons in distant ganglia projecting to the injected ganglion from elsewhere in the myenteric plexus also varied greatly. More strikingly, individual ganglia differed over a wide range with respect to whether the neurons in distant ganglia that provided them with terminals were situated in the oral, anal, or circumferential direction. Although the majority of projections were found to be from orally located ganglia, individual ganglia were observed that received predominantly or exclusively anal or oral projections. Others received mixtures of terminals from ganglia that were anal, oral, or circumferential. This anatomical heterogeneity in the location of afferent inputs to individual myenteric ganglia is probably reflected in a functional heterogeneity as well and will have to be taken into account in further studies of the physiology of the myenteric plexus. Individual ganglia of the plexus can no longer be taken as anatomically and functionally equ

ISSN:0092-7317    

DOI:10.1002/cne.902350407

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractThe organization of intrinsic axonal projections of principal neurons in the main olfactory bulb (MOB) was studied in hamsters by using wheat germ agglutinin‐horseradish peroxidase (WGA‐HRP) and fluorescent dyes. Punctate injections of either WGA‐HRP or fast blue (FB) that are restricted to small sectors on one side of the MOB produce comparably restricted fields of retrograde labeling on the opposite side. Label is found predominantly in superficially situated (middle and external) tufted cells that lie near and at the border between the external plexiform and glomerular layers. Few of the deeper middle tufted, internal tufted, or mitral cells and no external tufted cells that lie in the superficial two‐thirds of the glomerular layer are labeled in regions remote to the injection site. Anterograde transport of WGA‐HRP from the injection site labels axons that travel dorsally and ventrally in restricted bands through the internal plexiform layer and then terminate within this layer in the punctate sector on the opposite side that contains retrogradely labeled neurons. Such reciprocal projections between opposing regions of the medial and lateral sides of the MOB are found at all rostrocaudal and dorsoventral levels. When punctate injections of FB into the MOB are paired with restricted injections of a second fluorescent tracer (nuclear yellow or diamidino yellow dihydrochloride) into the appropriate sector of pars externa (pE) of the anterior olfactory nucleus, the punctate region of remote retrogradely labeled principal neurons is embedded within a topographically restricted longitudinal wedge of retrogradely labeled mitral and tufted cells that project extrinsically to or through pE. However, extremely few of these neurons are double‐retrogradely labeled. The results reveal the existence of an intrabulbar associational system in which principal neurons engage in point‐to‐point, reciprocal projections between opposing regions of the medial and lateral MOB. Moreover, the results indicate that this associational system largely arises from superficially situated tufted cells distinct from those that support bulbofugal projections into the topographically organized interbulbar commissura

ISSN:0092-7317    

DOI:10.1002/cne.902350408

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractPrevious studies have quantified growth and atrophy of the olfactory bulb and olfactory epithelium of the Sprague‐Dawley rat from maturity to senescence. Major events occurring in these structures include changes in the volume of mitral cells and changes in the number of septal olfactory receptors. These effects are large, consist of a growth phase followed by atrophy, and are temporally related in that events in the olfactory epithelium precede those in the mitral cells. A hypothesis of aging based on transneuronal effects would predict that these changes would be similarly transmitted to the next synaptic station in the olfactory pathway. Therefore, cells and synapses of the piriform cortex were studied in rats 3, 12, 18, 24, 27, 30, and 33 months of age. Alternate Vibratome sections through brains perfused with mixed aldehydes were processed for light and electron microscopy.No significant age effects were found for the volumes of cortical laminae Ia and Ib. Both numerical and surface density of synaptic apposition zones in layer Ia, formed primarily by mitral cell axons, were stable with age. A modest (18%) but significant decline in the proportion of layer Ia occupied by dendrites and spines was mirrored by an increase in the proportion of glial processes; no change in the proportion of axons and terminals was observed. Neither nuclear volume, nor soma volume, nor numerical density of layer II neurons changed with age.Thus, contacts made in the piriform cortex by mitral cell axons remain relatively stable in senescence, despite the marked volumetric changes in the mitral cell somata, changes which were confirmed again in this study. Age‐related dendritic regression in layer II neurons may be attributable to functional deafferentation subsequent to reduced receptor input to mitral ce

ISSN:0092-7317    

DOI:10.1002/cne.902350409

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractThe functional organization of the cochlear nucleus (CN) was studied with physiological recording and anatomical tracing techniques. Recordings were made from single CN neurons to examine their temporal firing patterns to tone burst stimuli and their frequency tuning characteristics. Recording loci of individual neurons were carefully monitored in order to understand how the functional properties of a cell relate to its location within the CN. We found that tonal frequencies were systematically represented in each of the three CN divisions (anteroventral, AVCN; posteroventral, PVCN; dorsal, DCN). Eight temporal response patterns were observed in CN neurons when stimulated at units' best excitatory frequencies (BF). With a few exceptions, neurons in each CN division could generate all eight firing patterns with different distributions for the three divisions. A focal injection of horseradish peroxidase (HRP), at the end of the physiological study, to a group of neurons possessing a similar BF in one CN division resulted in anterograde labeling of nerve terminals in the other two divisions at precisely the areas where the same frequency band was processed in these divisions. Labeled terminals in each division were closely congregated in the form of a thin slab. The slab orientation was division specific whereas its location was frequency specific, which could be predicted on the basis of physiological data. HRP injections into the DCN also resulted in retrograde labeling of somata in the AVCN and PVCN. On the other hand, only DCN neurons were retrogradely labeled when HRP was injected into the AVCN or the PVCN. These data showed how the three CN divisions are internally connected. Furthermore, retrogradely labeled cells occupied the same slabs where we found anterogradely labeled nerve terminals. Additionally, in a group of bats, HRP was injected into various functionally (i.e., BF) identified regions of the central nucleus of the inferior coliculus (IC) to clarify the type and location of CN projecting neurons. Retrogradely labeled cells in individual CN divisions likewise were arranged in slabs whose locations in the CN nuclei depended on the BFs of neurons at the injection site in the IC. These results show that slabs represent units of functional organization (i.e., tonal frequency, local connection and central projection) in the CN.

ISSN:0092-7317    

DOI:10.1002/cne.902350410

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.902350411

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY